1. Field of the Invention
The present invention relates to an image pickup apparatus including a shake correction unit arranged to correct an image shake.
2. Description of the Related Art
In modern cameras, important operations for image capture such as exposure and focus determination are automated, and the possibility for an unskilled photographer to cause an image pickup failure is extremely small. Also, recently, a camera provided with a system for preventing hand-induced image shake has been manufactured, and there are even fewer any factors for inducing the image pickup failure from the photographer.
Here, the known system for preventing image shake will be described. A camera hand movement at the time of image pickup is a vibration with a frequency of 1 to 10 Hz in usual cases. Then, in order to realize the image pickup of a photograph without being influenced by image shake even when such a hand movement is generated at the time of shutter release, it is necessary to detect the camera shake due to the hand movement and displace a shake correction unit provided with the correction optical system in accordance with the detected value.
Therefore, in order to capture the photograph without being influenced by image shake even when a camera shake is generated, first, it is necessary to detect the camera vibration precisely. Second, it is necessary to correct an optical axis change due to the hand-induced camera shake. The detection of the vibration (camera shake) can be performed in principle by detecting an acceleration, an angular acceleration, an angular rate, an angular displacement, and the like, and providing the camera with a processing or computation unit arranged to appropriately perform computation processing on the outputs. Then, based on the detection information, the shake correction unit for decentering the image pickup optical axis is driven to perform image shake correction.
FIG. 22A and FIG. 22B are a plan view and a lateral view of a conventional single-lens reflex camera, respectively. An image stabilizing system mounted to an interchangeable lens 90 which is attached to this single-lens reflex camera is arranged to perform the shake correction for a camera vertical shake and a camera lateral shake as illustrated in arrows 92p and 92y with respect to an optical axis 91. It is noted that the camera main body 93 includes a release member 93a, a mode dial (including a main switch) 93b, a retractable strobe light 93c, and a camera CPU 93d. In addition, reference numeral 94 denotes an image pickup element.
Reference numeral 95 denotes a shake correction unit arranged to perform the correction for the shakes in directions of arrows 92p and 92y by freely driving a correction lens 95a functioning as a correction optical system in direction of arrows 95p and 95y. Reference numerals 96p and 96y respectively denote gyros for detecting shakes about the arrows 92p and 92y, and arrows 96pa and 96ya indicate the respective detection sensitivity directions.
Signals output from the gyros 96p and 96y are subjected to computations in a lens CPU 97 and converted into shake correction target values of the shake correction unit 95. In synchronism with a switch to be turned ON through a half press of the release member 93a provided to the camera main body 93 (hereinafter referred to as switch S1: an operation switch arranged to instruct photometry and focusing for image pickup preparations), a drive target value is input to a coil of the shake correction unit 95 via a drive unit 98. With this configuration, the image shake correction is started.
In the image stabilizing system described with reference to FIGS. 22A and 22B, the gyros 96p and 96y are used for hand-induced shake detection. Not only the rotational movements about the arrows 92p and 92y (about the image pickup optical axis) but also the parallel movements illustrated in arrows 11pb and 11yb (parallel movements in the plane surface perpendicular to the image pickup optical axis) are applied to the camera main body 93. However, the rotational movements about the arrows 92p and 92y are dominant in a normal image pickup condition, and image degradation due to the parallel shakes illustrated in the arrows 11pb and 11yb is not apparent. For that reason, only the gyros 96p and 96y may be provided for hand-induced shake detection.
However, in the case of photography at an extremely close distance (in a photography condition where a photographing magnification ratio is high), the image degradation due to the parallel shakes illustrated in the arrows 11pb and 11yb cannot be ignored. For example, as in macro photography, a condition where the camera approaches an object at a distance of about 20 cm for picking up the image and a case where a focal distance in a photographic optical system is extremely large (for example, 400 mm) even when the object is located away from the camera by about 1 m are considered. In such cases, it becomes necessary to actively detect the parallel shake and drive the shake correction unit 95. Japanese Patent Laid-Open No. 7-225405 discloses a technology in which an accelerometer for detecting acceleration is provided to detect a parallel shake, and together with an output of a separately provided accelerometer, the shake correction unit 95 is driven.
FIGS. 23A to 23C illustrate image shake (image shift) amounts due to influences from the rotation shake and the parallel shake in a case of photography at an extremely close distance (1:1 magnification photography). The horizontal axis 101 represents an elapsed time after the camera is held, and the vertical axis 102 represents an image shake amount on the image pickup element 94. Here, the waveform 103 of FIG. 23A illustrates a time change in the image shake amount due to the parallel shake (parallel image shake). The waveform 104 of FIG. 23B illustrates a time change in the image shake amount due to the rotation shake (rotation image shake). Also, the waveform 105 of FIG. 23C illustrates the total image shake amount from the parallel shake and the rotation shake. From FIGS. 23A to 23C, the parallel image shake 103 and the rotation image shake 104 are changed over the elapsed time. However, particular attention should be given to the fact that the parallel image shake 103 is large in the case of photography at extremely close distances. Of course, the parallel image shake 103 has a small image shake amount when the object is far away or the photographing magnification ratio is small (while the zoom is set to the wide-angle end, for example). In the case of 1:1 magnification photography as in FIGS. 23A to 23C, the parallel image shake 103 causes a larger influence on the image degradation than the rotation image shake 104. Then, as the photographing magnification ratio larger, the effect is further increased. In order to correct this parallel image shake with high accuracy, it is necessary to provide a shake correction unit having a large correction stroke with which the shake amount can be corrected.
In the conventional shake correction unit, only a correction stroke limited to the correction for the rotation shake about the image pickup optical axis is provided. However, it is necessary to ensure a larger correction stroke for the correction for the parallel shake in the plane surface perpendicular to the image pickup optical axis. In the 1:1 magnification photography of FIGS. 23A to 23C, to correct both the rotation shake and the parallel shake at a high accuracy, a correction stroke at least two times larger than the conventional correction stroke is required. Here, the correction stroke and the size of the shake correction unit is in at least a proportional relation. This is because the shake correction unit (to be more specific, a correction lens) needs a twice larger stroke for performing spreading vibration with the optical axis set as the center and because the size of an actuator (a coil, a magnet, or the like) is accordingly enlarged and a drive margin is required. As a result, the weight increase of the actuator and the cost increase become also significant. As described above, if parallel shake is intended to be corrected in an application of the conventional method, the cost and weight increases are a disadvantage for apparatus intended for a normal consumer.